Modulating control apparatus



Aug. 26, 1947.

s; G. ISSERSTEDT 2,426,508 IODUIQATING CONTROL APPARATUS Filed March 26, 1943 mm; Saga-i=1 G. mama Patented Aug. 26, 1947 MODULATING CONTROL APPARATUS Siegfried G. Isserstedt, Toronto, Ontario, Canada, assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delaware Application March 26, 1943, Serial No. 480,671

The present invention relates to a simplified circuit arrangement for controlling a pair of electronic tubes so that either tube can be rendered non-conductive while the other tube is conductive. 1

More specifically, the present invention provides a simple circuit arrangement wherein a single source of'alternating power has a pair of electronic tubes connected acrossit in opposite manner, the cathode of a first tube and the anode of the second tube being connected to one side of the source of power, the anode of the first tube and the cathode of the second tube being connected to the other side of the source of power. The control electrodes of both tubes are then connected for example, to the electrical midpoint of a voltage divider which in turn is connected across the same single source of power: Thetype of electronic tubes preferably used are those of the cold cathode type wherein the starting or control electrode voltage must be somewhat greater than half the anode to cathode voltage. When such tubes are used in the manner above described, they will both be non-conductive since the control electrode voltage will be exactly one-half the anode to cathode voltage. Means are then provided to selectively raise the voltage on one control electrode While simul taneously lowering the voltage on the other control electrode, thereby rendering one of the tubes conductive while maintaining the other non-conductive. ihis selective raising of the voltage of one control electrode and lowering the voltage of the other can be accomplished in any number of manners, such as by shifting the point at which the control electrodes are connected to the voltage divider.

While I prefer to use that type of tube in which the tube is started only when the control electrode voltage is greater than one-half the anode to cathode voltage, it will readily be seen that other types of tubes requiring a positive starting voltage bearing a different relation to the anode to cathode voltage could be used. If, for example, a tube is used whose starting voltage is less than one-half the anode to cathode voltage, then when the voltage on each control electrode is one-half the anode to cathode voltage, both tubes will be conductive. Then, by simultaneously raising the positive voltage on the control electrode of one tube and lowering it On the other, the first will remain conductive and the second will be rendered non-conductive.

While the respective voltages of the control electrodes'of the two tubes can be shifted in the '9 Claims. (01. 172-239) manner above outlined, I prefer to accomplish this by including the secondary of an input transformer in the circuit connecting the control electrodes to the electrical mid-point of the voltage divider and then supplying power to the primary of such input transformer from the same single source of power. The voltage applied to the primary of the input transformer and its phase relation to that of the source of power can be determined in any desired manner but I preferably bring this about through the use of a bridge circuit, which bridge circuit may be of the self balancing type in order that a proportioning or modulating system of control will result.

In the event that the extra voltage is obtained through the use of an input transformer, it will also be apparent that tubes requiring a negative control electrode voltage to render them non-conductive could be used, the necessary high negative voltage to cut one or the other of them off being supplied by the use of a sufficientl stepped-up input transformer.

It therefore follows that it is an object of the present invention to provide a simplified circuit for a pair of electronic tubes by connecting their control electrodes to a single voltage divider connected across the same source of power that supplies the oppositely connected anodes and cathodes of the tubes and selectively changing the relative voltages applied to the control electrodes by the voltage divider so as to simultaneously make one tube conductive and the other nonconductive.

In the form of my invention to be disclosed in detail hereinafter, the bridge circuit is unbalanced bya temperature responsive device and the tubes in turn control reversible electric motor means which operate to return the temperature toward the desired value and simultaneously the bridge is rebalanced.

An object of the present invention then is to provide improved control apparatus ofthe type wherein a condition responsive device controls a reversible motor. I Another object of the present invention is to provide a condition responsive motor control system in which the motor is controlled'byan im proved and simplified electronic; amplifiercircuit.

A further object is to provide such asystern utilizing gaseous discharge tubesof the cold cathode type in the electronic amplifier. f

Other objects and advantages. of my invention will become apparent from}; consideration of the appended claims, specification, and drawing, in which the single figure represents a tem- The valve may be positioned by means of a stem Ii. The end of stem ii is pivotally attached to a link l2, whose other end is pivotally attached to a disc 12, ilxed on ashaft i4 so as to rotate therewith. Shaft i4 is driven, through a gear:

train schematically indicated at Il,'by a motor i8. Motor I6 is shown as being of the split phase type, and is provided with a pair of field windings l1 and i8. displac d in space phase by approximately 90", as is conventional with motors of that type.

Motor It also drives, through the shaft i4 and a second gear train schematically indicated at 20, a shaft 2i, on which is fixed a slider 22, which cooperates with a slidewire resistance indicated at 23.

A second slidewire resistance 24 is provided, hawng a slider 25 cooperating therewith. 'Slider 25 is moved with respect to slidewire 24 by a bimetallic thermostatic element 26. The respective ends of the slidewires 22 and 24 are connected electrically, as are the sliders 22 and 25. The slidewires 23 and 24, their sliders 22 and 25, and their connections form a bridge circuit 21, of the Wheatstone type.

The connection between the left hand end of slidewires 23 and 24 may be traced from the left hand end of slidewire 24 through conductors 30, 2i and 32 to the left hand end of slidewire 23. A corresponding connection may be traced from the right hand end of slidewire 24 through conductors 23, I4 and I! to the right hand end of slidewire 22. The connection between the sliders may be traced from slider 25 through bi- 'metallic element 28, a conductor 30, primary winding 21 of an input transformer Ill, and a conductor 39 to slider 22.

Conductors 8i and 84, which may be said to Y include the input terminals or the bridge circuit 21, are connected to the opposite terminals of a secondary winding 40, of a transformer 4| having a primary winding 42. Primary winding 42 is connected to any suitable source of alternating current, such as lines 43 and 44.

A voltage dividing resistance 45 is connected between lines II and", and is provided with a mid-point tap, as indicated at 48.

Input transformer 28 is provided with a secondary winding 41.

A pair of electric discharge devices 50, ll are provided having cathodes 52, 88, anodes 54, ll, and control electrodes and 51, respectively. These discharge devices, which may be of the type known as Western Electric Type 346A, are gas filled discharge tubes of the cold cathode type. Such tubes are commonly operated with an anode to cathode potential which is not sumcient to start a discharge between the anode and cathode, but is suiiicient to maintain such a discharge once lt is started. The discharge is customarily initiated by the control electrode, which is sometimes referred to as a starting anode. The control electrode is so constructed that the voltage necessary to start .a discharge between the cathode and control electrode is much smaller than the voltage required to start adischarge between the cathode and anode. Furthermore, such tubes are built so that when a discharge is initiated between the cathode and the control electrode, it is immediately transferred to the cathode and anode, and thereafter maintained by the anode to cathode voltage. The general characteristics oithis type of device are well known in the art, and it is believed unnecessary to discuss them further here.

The particular type of tube mentioned, that is, Western Electric Type 346A, has an additional characteristic which renders it particularly suitable for the control circuit described herein. This characteristic is that the voltage which mus, be supplied to the control electrode to initiate a discharge in the tube is slightly greater than one-half of the anode to cathode voltage.

The peculiar adaptability of this characteristic to the present control system will be brought out more clearly in connection with the operation of the system.

Cathode 52 of discharge device 50 is connected by a conductor to supply line Ii. Anode 54 is connected to supply line 24 through a conductor 6|, a relay winding 62, in parallel with a condenser 82, and a conductor 64.

Cathode 52 of discharge device vll is connected through a conductor 6! to supply line I4, while anode ii is connected to supply line Ii through a conductor 68, a relay winding 61 in parallel with a condenser 88, and a conductor 69.

Control electrode 66 is connected to a conductor 10, and control electrode 51 is connected to a conductor 1|. The conductors ,10 and 1i are both connected, through a conductor 12, secondary winding 41 of input transformer 88, and a conductor 12 to mid-point 46 of voltage dividing resistor 45.

Relay winding 02 forms a part of a relay 14, which also includes a switch arm 15, operable upon energization of winding 62 into engagement with astationary contact 16. Similarly, relay winding 81 forms a part of a relay '0, which also includes a switch arm Ii, operable upon energization of winding 61 into engagement with a stationary contact 42.

Operation v When the parts are in the position shown in the drawing, the sliders 22 and 25 are at the mid-point of their respective slide wire resistances 22 and 24. The two sliders are therefore at the same potential and no current flows through the connection between them, which may be termed the output circuit of the bridge 21. The bridge circuit 21 is therefore balanced.

Under these conditions, no current flows in primary winding 21 of input transformer 38, and no potential is induced in the secondary winding 41. N and 51 is substantially the same as the potential of mid-point 40 of voltage divider 45 to which the control electrodes are connected. There is then no current flow through either of the devices 40 and I, since, as previously described, it is necessary that a potential greater than one-half the anode to cathode potential be applied to the control electrodes in order initiate a discharge.

It will be noted that the discharge devices 54 and I are connected in opposite senses to the supply lines II and 34. Since the discharge devices II and ii, in accordance with the well known characteristic of such devices, can conduct current only in one direction, it will be apparent that the discharge device 50 can be conductive only on the half cycles of alternating current during which the supply line ll con- The potential of the control electrodes nected to cathode 52 is negative and the supply line 34 connected to anode 54, is positive. n the other hand, the discharge device is so connected that it is conductive only on the half cycles when the supply line 3| is positive and the supply line 34 is negative.

When a discharge of either of the devices 58 or.5| is initiated, it is maintained until the anode to cathode potential of the particular device drops to zero, which occurs at the end of the half cycle during which the discharge was initiated. Current flow through the particular device will then cease, for at least one half cycle. If the control electrode still retains the potential necessary to initiate a discharge when the next positive half cycle occurs, the discharge will again be initiated. Therefore, it may be seen that the current flow between the anode and cathode of these devices takes place in a series of intermittent pulses. The condensers 63 and 68 are connected in parallel with the relay windings 62 and 61, respectively, in order that these intermittent pulses may be smoothed by thedischarge of the condenser during the half cycle when the tube is non-conductive, thereby maintaining the relay energized without chattering of its contacts.

Now let it be assumed that the temperature adjacent the bimetallic element 26 decreases, thereby moving slider 25 to the left of the slide wire resistance 24 as indicated by the legend in the drawing. When this takes place, sliders 24 and 22 are at differentpotentials, and a current flows from slider 25 to slider 22 through the output circuit of the bridge 21 including primary winding 31 of input transformer 38,

Consider the effect of such a displacement of slider 25 during the half cycles when supply line 3| is positive with respect to supply line 34. Since slider 25 has moved to the left, it has become more positive than slider 22, and therefore the upper terminal of primary winding 31 is positive with respect to its lower terminal, Since the voltage and current in the secondary winding of any transformer are substantially 180 out of phase with the voltage and current in the primary winding, itwill be apparent that the upper terminal of secondary winding 41 of input transformer 38 is at this time negative with respect to the lower terminal. The lower terminal of transformer secondary winding 41 is connected to control electrode 51 through conductors 12 and 1|. The control electrode 511s therefore at a potential more positive than that of mid-point 46 of voltage divider 45 by the amount of the voltage across secondary winding 41. The voltage between control electrode 51 and cathode 53 is therefore greater than one-half of the voltage between anode 55 and cathode 53. Since the discharge device 5| has a characteristic such that a discharge is initiated when the control electrode to cathode voltage is slightly greater than one-half of the anode to cathode voltage, it will be apparent that under the'condition described, the discharge device 5| will be rendered conductive. The device 58 is of course non-conductive during this half' cycle, because its cathode is positive with respect to its anode. During the opposite half cycles, when device 58 might be conductive, the polarity of the voltage across secondary 41 of input transformer 38 is reversed; so that both control electrodes 56 and 51 are more negative than the midpoint tap 46 of resistance 45, and both devices 58 and 5| are non-conductive.

When discharge device 5| becomes conductive on alternate half cycles, the winding 61 of relay 88 .is energized sufficiently to move switch arm 8| into engagement with contact 82. This completes an energizing circuit for windings l1 and I8 of motor l6. The energizing circuit for winding I1 may be traced from supply line 3| through winding |1, conductors 83 and 84, contact 82, switch arm 8|, and conductor 85 to supply line 84. The energizing circuit for winding l8, may be traced from supply line 3| through winding l8, a, conductor 86, a condenser 81, conductor 84, contact 82, switch arm 8|, and conductor 85 to supply line 34. Since condenser 81 is in series with winding |8,' while winding i1 is connected directly across the line, the current flow through winding |8 will be substantially. out of phase with the current flow through winding |1, thereby determining the direction of rotation of motor I6. The gear trains I5 and 28 are so constructed that rotation of motor IS in this direction will move valve |8 toward open position and will rotate shaft 2| clockwise, thereby moving slider 22 to the left across the slide wire 23, This operation of motor l6 continues until slider 22 has been moved to the left a sufiicient amount so that its potential is substantially the same as that of slider 25, whereupon the current flow through transformer primary winding 31 ceases, and control electrodes 51 again assume the potential of midpoint 46 of voltage divider 45. The bridge circuit 21 is then said to be rebalanced. On account of its function, slider 22 and the slide wire 23 are sometimes referred to as the rebalancing potentiometer.

Now consider the operation of the system when the slider 25 moves to the right along the slide wire 24. ,During the half cycles when supply line 34 is positive with respect to supply line 3|, it will be readily understood that this unbalance of the bridge circuit induces in the secondary winding 41 of input transformer 38 a potential which renders control electrodes 56, and '51 more positive than the midpoint 46 of voltage dividing resistor 45. This takes place during the half cycles when discharge device 58 may be conductive, and thereby initiates a discharge of the device 58, energizing relay 62.

Energization of relay winding 62 causes switch arm 15 to be'moved into engagement with contact 16, thereby completing an energizing circuit fOr windings l1 and I8 of motor 6. This energizing circuit for winding |1 may be traced from supply line 3| through winding l1, conductor 83, condenser 81, a conductor 88, contact 16, and switch arm 15, to line 34. 4 The energizing circuit for winding l8 may be traced from line 3| through winding I8, conductors 86 and 88, contact 16, and switch arm 15 to line 34. Winding i8 is now connected directly across the line, while winding I1 is connected in series with conductor 81. The phase relations between the currents in windings l1 and I8 are now opposite to those existing under the condition previously described, and the direction of rotation of motor I6 is therefore opposite to the previous direction. Valve |8 is driven towards closed position, and slider 22 is moved to the right across slide wire 23 to rebalance the bridge circuit 21.

While I have shown and described a preferred embodiment of my invention, it will be readily apparent to those skilled in the art that other modifications will occur, and Iv therefore wish my invention to be limited only by the scope of the appended claims.

I claim as my invention:

1. A control system, comprising in combination, a pair of electrical discharge devices, each including an input circuit and an output circuit, and having a characteristic such that the output circuit is non-conductive until a potential greater than one-half'the output circuit potential is, applied to the input circuit, means adapted to connect the output circuits of said discharge devices in opposition across substantially the same portion of a source of alternating electrical-energy, means connecting both said input circuits to a point having a potential substantially equal to the median potential 01' said source, a balanced electrical network connected to said source, means responsive to a condition indicative of the need for operation oi said control devices for unbalancing said network, means connectin said network with said input circuits so as to introduce therein a potential variable in polarity in accordance with the direction of unbalance of said network, and electrical means associated with the output circuits of said devices so as to be energized selec tively in accordance with the relative conductivity oi said-devices.

2. A control system, comprising in combination, a pair of electrical control devices to be selectively energized, a pair of electrical discharge devices, each including an input circuit and an output circuit, and having a characteristic such that the output circuit is non-conductive until a potential greater than one-half the output circuit potential is applied to the input circuit, means adapted to connect the output circuits of said discharge devices in opposition across substantially the same portion of a source of alternating electrical energy with one of said control devices in series with each output circuit, means connecting both said input circuits to a point having a potential substantially equal to the median potential or said source, a balanced electrical network adapted for connection to said source, means responsive to a condition indicative of the need for operation of said control devices for unbalancing said network, and connections between said network and said input circuits so as to introduce therein an alternating potential substantially corresponding in phase to the output circuit potential of one or the other or said discharge devices, depending upon the direction 01' unbalance oi. said network.

3. A control system, comprising in combination, a pair of electrical control devices to be selectively energized, a pair oi electrical discharge devices, each including an input circuit and an output circuit, and having acharacteristic such that the output circuit is non-con ductive until a potential greater than one-half the output circuit potential is,..ap"plied to the input circuit, means adapted'to connect the output circuits oi said discharge devices in opposition across substantially the same portion oi a source of alternating electrical energy with one of said control-devices in series with each output circuit, means connecting both said input circuits to a point having a potential substantially equal to the median potential of said source, a balanced electrical network having input terminals and output terminals, connections between said input terminals and said source, means responsive to a condition indicative of the need for operation of said control devices for unbalancing said network, a transformer having a primary winding and a secondary winding, connections between said network output terminals including said primary winding, and

connections-between said secondary winding and tion, a pair of electrical control devices to be selectively energized, a pair of electrical discharge devices, each including an input circuit and an output circuit, means adapted to connect the output circuits of said discharge devices in opposition across substantially the same portion of a source of alternating electrical energy with one oi said control devices in series with each output circuit, an impedance connected across said source, a connection between both said input circuits and the midpoint of said impedance, and means for introducing in said connection a potential variable in phase.

5. In a control system, in combination, a pair oi electrical control devices to be selectively energized, a pair 0! gaseous electric discharge devices adapted to be connected oppositely across the same portion 01 a source oi alternating electrical energy, each said discharge device including an anode, a cathode, and a control electrode and having a characteristic such that a discharge between anode and cathode is initiated when the potential between anode and control electrode is slightly greater than one-half of the potential between anode and cathode, a connection between both said control electrodes and a, point having a potential substantially equal to the median potential of said source, means for introducing an alternating control potential in said connection, and means responsive to a condition indicative of the need for operation of said control devices for varying the phase of said control potential.

6. A control system, comprising in combination, a pair of electrical control devices to be selectivel energized, a pair of electrical discharge devices, each including an input circuit and-an output circuit, and having a characteristic such that the output circuit is non-conductive until a potential having a positive value greater than a predetermined proportion of the output circuit potential is applied to the input circuit, means adapted to connect the-output circuits of said discharge devices in opposition across the same portion of a source of alternating electrical energy with one 01' said control devices in series with each output circuit, impedance means connected across said same portion of said source of alternating energy, means connecting said input circuits to said impedance means to supply to said input circuits an alternating potential equal in magnitude to said predetermined proportion of said output circuit potential, and means for applying an additional variable potential derived from said source to both said input circuits. 7

7. Control apparatus, comprising in combination, a pair of conductors adapted for connection to opposite terminals of a source of alternating electrical energy, a pair or electric discharge devices having input circuits and output circuits and having similar characteristics such that said output circuits are either in a. substantially nonconductive state or a substantially conductive state, depending on the potential applied to said input circuits, means connecting said output circults to said pair of conductors inopposite senses, means for applying a potential substantially equal to the median potential of said source to both said input circuits so as to tend to maintain both said output circuits in the same state, means for applying an additional potential derived from said source to both said input circuits, means for varying said additional potential so as to selectively change the state of either of said output circuits, and means controlled by said output circuits.

8. In combination, a source of power, a first impedance connected across said source of power and having a tap at substantially the midpoint thereof, a pair of further impedances connected in parallel with said first impedance across said source of power, a movable tap associated with each of said further impedances, said further impedances constituting a balanceable bridge with said movable taps constituting the ouptput terminals thereof, a pair of electronic discharge devices oppositely connected across said source of power in parfilel with said first impedance, each of said discharge devices having an anode, a cathode, and a control electrode and having a characteristic such that a discharge between anode and cathode is initiated when the potential between anode ai rd control electrode is slightly greater than one-half of the potential between anode and cathode, a connection between both said control electrodes and said tap of said first impedance so as to tend to maintain both electrodes at a, potential with respect to their cathodes equal to substantially hall of the potential .between the anodes and cathodes, and means for introducing into said connection a voltage determined hy the unbalance voltage of said bridge as measured across said movable taps.

9. In combination, an alternating source of power, a first impedance connected across said source oi! power and having a tap at substantially the midpoint thereof, a pair of further impedances connected in parallel with said first impedance across said source of power, a movable tap associated with each of said further impedances, said further impedances constituting a balanccable bridge with said movable taps constituting the output terminals thereof, a pair of electronic discharge devices oppositely connected across said source of power in parallel with said first impedance, each of said discharge devices having an anode, a cathode, and a control electrode and having a characteristic such that a discharge between anode and cathode is initiated when the potential between anode and control electrode is slightly greater than one-half of the potential between anode and cathode, a connection between both said control electrodes and said tap of said first impedance so as to tend to maintain both electrodes at a potential with respect to their cathodes equal to substantially half 01 the potential between the anodes and cathodes, and a transformer having a primary winding connected to said movable taps and a secondary winding connected in series with said connection so as to introduce into said connection a voltage determined by the unbalance voltage of said bridge.

SIEGFRIED G. ISSERSTEDT.

REFERENCES CITED The following references are of record in the file oi this patent:

\ UNITED STATES PATENTS Number Name Date 1,942,587 Wmtmam Jan. 9, 1934 1,966,235 Dawson July 10, 1934 2,078,645 Swingle "Apr. 2'7, 193? 

